1. Field of the Invention
The present invention pertains to airfoil structures of composite material used in part of an aircraft elevator or wing, for example, as well as to methods of forming such airfoil structures. More particularly, the invention relates to airfoil structures of composite material which are easy to manufacture and provide a high peeling strength as well as to their forming methods.
2. Description of the Related Art
FIGS. 19 to 21 show an elevator surface structure of a related art aircraft using composite materials, in which the aircraft's elevator 1 is constructed by individually forming an upper skin 2, a lower skin 3, a spar 4 and ribs 5 using the composite materials and, then, assembling them by use of fastener means 6, such as bolts and nuts.
The related art aircraft elevator 1 has such problems that it involves a large number of principal constituent components, requiring high manufacturing costs for those components, and because they need to be assembled by using a number of fasteners, assembling component costs are also high. A further problem is that it is necessary to make many holes for fitting the fasteners, resulting in an increase in man-hours required for assembly work.
Box-structure airfoils in which a frame is produced by previously fastening spars and ribs with clips to reduce the man-hours required for assembly with fasteners and upper and lower skins are bonded to the frame are disclosed in European Patent Bulletin Publication No. 485027 and published U.S. Pat. No. 5,216,799, for example.
Although it has been attempted to reduce the number of fasteners and the man-hours required for assembly by assembling the individual skins by bonding in the aforementioned box-structure airfoil, the number of components is not actually reduced because the principal components have the same construction as those of the related art. Further, as it is necessary to previously join the spars and ribs with fasteners and then adjust mating surfaces by machining flange surfaces of the spars and ribs after frame assembly, there arises a problem that man-hour requirements are increased.
Also, structures shown in FIGS. 22 and 23 in which a frame 7 and a skin 8 are bonded by using an adhesive 9 have a low out-of-plane peeling load (peeling load exerted in a direction perpendicular to the skin 8) compared to fastener assembly, and this would pose a problem related to strength.
Although it is advantageous for improving the peeling strength if the frame 7 has an I-shaped cross section rather than a U-shaped cross section, the frame 7 of the I-shaped cross section entails approximately twice as high manufacturing cost as the frame 7 of the U-shaped cross section, thus developing a problem of increased cost.